Articulated vehicle wheel tracking mechanism

ABSTRACT

The invention provides a trailer for use as part of an articulated vehicle ( 15 ) with improved cornering characteristics. The trailer includes: a main chassis ( 18 ) connectable to a wheeled section ( 16 ) of the vehicle immediately ahead of the trailer so that the trailer is rotatable relative to the wheeled section ( 16 ) about a substantially upright first axis ( 19 ) in the main chassis ( 18 ); a sub-chassis ( 20 ) having ground-engaging wheels ( 21 ) mounted thereto, the sub-chassis ( 20 ) being connected to the main chassis ( 18 ) and pivotable about a substantially upright second axis ( 23 ) in the main chassis ( 18 ); and stop means arranged for limiting rotation of the sub-chassis ( 20 ) about the second axis ( 23 ) and away from a position of a longitudinal alignment with the main chassis ( 18 ). The stop means is movable responsively to relative rotation of the wheeled section ( 16 ) and the main chassis ( 18 ) about the first axis ( 19 ). In a preferred arrangement, some wheels on the sub-chassis ( 20 ) are steerable responsively to rotation of the sub-chassis ( 20 ) about the second axis ( 23 ).

FIELD OF THE INVENTION

[0001] This invention relates to articulated vehicles of the type havinga prime mover, or tractor, and one or more trailers.

[0002] An often-seen vehicle in this class is the so-called“semi-trailer”, having a prime mover with a single trailer, the trailerusually being longer than the prime mover. The trailer typically hasone, two or three non-steerable axles adjacent to its rear end and aturntable at its front end which mates with a cooperating arrangement(sometimes termed a “fifth wheel”) on the prime mover so that thetrailer can articulate about a substantially vertical axis of the primemover for turning.

[0003] A number of problems arise with articulated vehicles of thistype. One of these is manoeuvring. A significant width of road isrequired for turning corners, for example, by comparison with shorternon-articulated vehicles, and driver skill requirements may be high,because a trailer's fixed wheels generally “off track”, i.e. fail tofollow the path taken by the wheels of the prime mover. At least atcomparatively low speeds, the trailer wheels normally track inside thepath of the prime mover. These problems can be particularly acute oncity roads as a turning vehicle in one lane may encroach on anotherlane. At high speeds tracking of the trailer wheels outside the path ofthe prime mover is known. However, the problem of off-tracking atcomparatively low speeds is the more practically significant one, andmuch effort has been expended in trying to provide practical solutions.

[0004] A further problem is tyre wear due to scuffing or scrubbing onthe road surface. When multiple, parallel axles are provided on thetrailer, as is common, it is not possible for the axes of rotation ofthe trailer's wheels to converge at the centre of the trailer's turningcircle, so that tyre scrubbing is inevitable. Apart from excessive tyrewear, scrubbing, leads to increased fuel consumption, and may also leadto poorer braking and roadholding.

[0005] A still further problem with semi-trailers is manoeuvrabilitywhen reversing. In tight quarters particularly, it can be difficult tomanoeuvre such a vehicle as required.

[0006] The present invention is directed to at least alleviating theproblems set out above. Other attempts have been made to address theseproblems, and many of these suffer from a further problem, namely theneed for major modifications to the prime mover, by comparison with a“standard” prime mover such as would be used for conventionalsemi-trailers. As it is commonly required that a given trailer be towedby many different prime movers, systems not requiring majormodifications to the prime mover are desirable, and the presentinvention provides such a system.

[0007] It should be noted that the off-tracking problem arises withvehicles having multiple trailers behind a prime mover. The inventiondisclosed below is also applicable in some aspects to such vehicles.Two-trailer articulated vehicles are often used in metropolitan areas,and vehicles having three or more trailers are also known, although dueto their limited manoeuvrability they are normally confined tonon-metropolitan roads and off-road applications.

PRIOR ART

[0008] Various approaches have been proposed for solution, or partialsolution, of the closely related problems of tracking and tyrescrubbing, but a range of disadvantages appear to have prevented theirwidespread adoption for ordinary articulated vehicles.

[0009] One approach to reducing tyre scrubbing on trailers, but which isof very limited usefulness in improving tracking, is to provide for somewheel/axle assemblies to have fixed (non-steerable) wheels but to befree to pivot as a whole about a vertical axis placed ahead of the axlein the direction of travel, thereby to have a castoring action. See forexample Sibbald, PCT/AU94/00743, and Becker and Ennor, Australian PatentNo. 664919. Arrangements in this class must have some means for lockingthe wheel/axle assemblies in a straight-ahead orientation, or forshifting the vertical axis behind the axle, to allow for reversing.Castoring wheel assemblies have not found significant favour inpractice.

[0010] The problem of reducing off-tracking of trailers has been mostcommonly addressed by providing arrangements whereby at least some oftheir wheels are “steered” during turns in an opposite sense to thesteering of the prime mover. That is, if the prime mover begins a turnto the right, some wheels adjacent to the rear of the trailer areoriented to displace the rear of the trailer to the left, i.e. to theoutside of the turn. If the degree of such orientation is suitablychosen, the rear of the trailer may be caused to follow substantiallythe path taken by the prime mover. Many of these arrangements also tendto reduce the problem of tyre scrubbing, although the degree ofreduction varies widely among the various proposals.

[0011] Some of these improved tracking systems actively orient thetrailer wheels, or some of them, in a way responsive to articulationbetween the trailer and the prime mover or responsive to steering of theprime mover's front wheels. These systems generally require a primemover significantly different from a conventional one. These vary fromvery simple mechanical systems such as that of Humes, U.S. Pat. No.3,533,644, to more complex mechanical and/or hydraulically actuatedsystems, for example, the system described by Kramer, U.S. Pat. No.4,982,976.

[0012] In another class of improved tracking arrangements, reliance isplaced on the tendency of the trailer's wheels to continue movingforward as the front of the trailer is displaced laterally in a turn.The consequent difference between the original path of these wheels andthe new path of the trailer provides an input which can be harnessed toorient the trailer wheels to the degree required for correct tracking ofthe prime mover's path. Curry (U.S. Pat. No. 3,899,188) describes such asystem with a fixed wheel/axle assembly (i.e. one in which the wheelsare not orientable relative to the axle) at the rear of a sub-chassisand a wheel/axle assembly with individually-steerable wheels at thefront of the sub-chassis. Penzotti (U.S. Pat. No. 5,246,242) describes avariation having two fixed axle assemblies on a sub-chassis. Both ofthese systems rely on relative movement between the trailer's mainchassis and a sub-chassis due to turning for their action, and neitherrequires significant modification of the prime mover compared to aconventional one. This is advantageous. Both require provision forlocking of the sub-chassis to the main chassis of the trailer in astraight-ahead condition for reversing purposes. Mitchell(PCT/GB97/02008) describes a comparatively complex system with two setsof individually steerable wheels and a fixed wheel/axle assembly on asub-chassis, and having provision for providing different and selectablesteering responses in forward and reverse travel.

[0013] In one aspect, the invention disclosed herein is in this class,as reliance is placed on the tendency of the trailer's wheels tocontinue moving forward as the front of the trailer is displacedlaterally in a turn to control orientation of wheels on the trailer.

SUMMARY OF THE INVENTION

[0014] In a first aspect, the invention provides a trailer for use aspart of an articulated vehicle, the trailer including:

[0015] a main chassis connectable to a wheeled section of the vehicleimmediately ahead of the trailer so that the trailer is rotatablerelative to said wheeled section about a substantially upright firstaxis in the main chassis;

[0016] a sub-chassis having ground-engaging wheels mounted thereto, saidsub-chassis being connected to the main chassis and pivotable about asubstantially upright second axis in the main chassis;

[0017] stop means arranged for limiting rotation of said sub-chassisabout said second axis and away from a position of longitudinalalignment with said main chassis,

[0018] wherein said stop means is movable responsively to relativerotation of said wheeled section and said main chassis about said firstaxis.

[0019] In a particularly preferred aspect, the trailer has a pluralityof pairs of ground engaging wheels longitudinally spaced apart on saidsub-chassis and includes steering means responsive to relative rotationof said sub-chassis and said main chassis about said second axis forsteering at least one said pair relatively to said sub-chassis in such asense as to tend to align said sub-chassis longitudinally with said mainchassis.

[0020] In one embodiment, the trailer further includes:

[0021] a yoke mounted to said main chassis and bearing against said stopmeans; and

[0022] connecting means whereby said yoke is connected to saidsub-chassis and movable in said main chassis responsively to rotation ofsaid sub-chassis about said second axis.

[0023] Preferably, said yoke is mounted for substantially longitudinalmovement in the main chassis and has a slide surface extending in adirection substantially transverse to the main chassis;

[0024] a slider is included in said stop means and mounted in said mainchassis so as to pivot around said first axis in concert with saidwheeled section pivoting about said first axis; and

[0025] said slide surface bears against said slider.

[0026] In a particulary preferred embodiment, the trailer furtherincludes:

[0027] a member mounted to said main chassis for movement relativethereto responsively to said rotation of said sub-chassis about saidsecond axis; and

[0028] movement transmitting means whereby said movement of said membercauses a corresponding movement of a follower means and saidcorresponding movement is limited according to the position of said stopmeans.

[0029] Preferably, said movement transmitting means includes first andsecond hydraulic actuators operatively interconnected by hydraulic fluidconduits so that actuation of said first actuator by said movement ofsaid member produces a corresponding movement by said second actuator ofsaid follower means.

[0030] Preferably also, the stop means includes a cam arranged to rotatein said main chassis about said first axis and adapted to be coupled tosaid wheeled section.

[0031] The invention also provides a trailer for use as part of anarticulated vehicle, the trailer including:

[0032] a main chassis;

[0033] a sub-chassis pivotable about a substantially upright first axisin the main chassis;

[0034] at least one assembly pivotable about a substantially uprightsecond axis in the sub-chassis and including a rigid axle with groundengaging wheels thereon; and

[0035] a link secured to said assembly and said main chassis,

[0036] whereby in response to a rotation in one sense of saidsub-chassis about said first axis, said link rotates said assembly aboutsaid second axis in such a sense as to steer said wheels in such adirection as to tend to reduce said rotation of sub-chassis duringforward motion of said trailer.

[0037] The invention further provides an articulated vehicle including atrailer in any of the above embodiments or forms.

[0038] The invention still further provides apparatus for operating aground wheel steering means of a trailer mountable to a fifth wheelassembly of an articulated vehicle, said fifth wheel having a slot inwhich a kingpin of said trailer is receivable and retainable, saidapparatus including:

[0039] a member arranged to pivot about an axis of said kingpin;

[0040] means whereby said ground wheel steering means is operatedresponsively to pivoting of said member about said axis;

[0041] drive means secured to said member and which depend from saidtrailer and are receivable in said slot.

[0042] Non-limiting embodiments of the invention in its several aspectswill now be described in detail with reference to the following Figures,of which:

[0043]FIG. 1 is a schematic plan view of a prior art semi-trailervehicle;

[0044]FIG. 2 is a schematic plan view of a modified semi-trailervehicle;

[0045]FIG. 3 is a schematic plan view of a semi-trailer according to theinvention;

[0046]FIG. 4 is a schematic plan view of a further semi-traileraccording to the invention;

[0047]FIG. 5 is a schematic plan view of the vehicle shown in FIG. 3 instraight-ahead configuration;

[0048]FIG. 6 is a schematic partial plan view of the vehicle shown inFIG. 5, in a turning configuration;

[0049]FIG. 7 is a cross-sectional view of a component of the vehicleshown in FIG. 6;

[0050]FIG. 8 is a schematic, partial elevation taken in the direction ofarrow “350” in FIG. 6;

[0051]FIG. 9 is a schematic partial plan view of the vehicle shown inFIG. 3;

[0052]FIG. 10 is a schematic partial plan view of the vehicle shown inFIG. 4;

[0053]FIG. 11 is a partial cross-section of the vehicle shown in FIG. 6taken at station “BB” therein;

[0054]FIG. 12 is a partially exploded perspective view of a part of thevehicle shown in FIG. 3.

[0055]FIG. 13 is a schematic partial plan view of the vehicle shown inFIG. 3, with an alternative variable stop means according to theinvention. One part of the Figure is an enlarged view of detail “A” inFIG. 13.

[0056]FIG. 14 is a schematic partial plan view of the vehicle shown inFIG. 3, with an alternative variable stop means according to theinvention.

[0057]FIG. 15 is a perspective view of a sub-chassis for use in theinvention.

[0058]FIG. 16 is a partial cross-section of the trailer of the vehicleshown in FIG. 3, taken on the longitudinal centreline thereof, whenfitted with an alternative variable stop means according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0059] In the following description, the main inventive concept of avariable stop means applied to automatic steering of a sub-chassis on atrailer is described, first generally and then by reference to twodetailed embodiments. Certain locking arrangements are then described. Aparticularly preferred form of sub-chassis is then described, havingindividually steerable axle assemblies. This is usable with eitherembodiment of the variable stop means. Finally a novel arrangements forconnection of a trailer according to the invention to a prime mover's“fifth wheel” is described.

[0060]FIG. 1 shows a schematic plan view of an articulated vehicle 1 ofthe “semi-trailer” type, having a prime mover 2 and a trailer 3pivotally connected to each other at a pivot 4 so that the prime moverand trailer can rotate relative to each other about an upright axis 5.Vehicles such as vehicle 1 are well known in the art. Both the primemover 2 and the trailer 3 are shown in outline only, with mechanicaldetail omitted. The prime mover 2 has a pair of steerable wheels 6 andtwo pairs of driven ground-engaging wheels 7, although other numbers ofdriven wheels are also known. The trailer 3 has three pairs ofnon-driven ground-engaging wheels 8 near its rear end, which are notsteerable. That is, their axes of rotation 9 are held substantiallytransverse to the length of the trailer 3. This arrangement is wellknown and conventional in the art. Semi-trailers are also commonly usedwhich have two pairs or even one pair of rear wheels instead of thethree pairs 8.

[0061] The vehicle 1 is shown in FIG. 1 established in a turn whiletravelling forward. The arrow 201 shows the direction of travel. A point10 in the vicinity of the wheels 8 is travelling on a curved path 11whose radius 12 is less than the radius 13 of a path 14 traced out bythe pivot 4. This phenomenon is found in practice, at least at low andmoderate speeds, and is the form of “offtracking” most commonly seen inpractice. Apart from presenting difficulties in manoeuvring, it involvesscrubbing of at least some (and in general all) of the wheels 8 as theyare simultaneously rolling and sliding sideways.

[0062]FIG. 2 shows, also in a schematic plan view, a vehicle 15 which issimilar to the vehicle 1. Vehicle 15 has a prime mover 16 and a trailer17. The trailer 17 includes a main chassis 18 mounted to the prime mover16 for pivotal relative rotation about an upright axis 19. The mainchassis 18 is also pivotally mounted for relative rotation about anupright axis 23 on a sub-chassis 20, to which, in turn, there aremounted three pairs of wheels 21. The wheels 21 are not steerablerelative to the sub-chassis 20, their axes of rotation 22 lyingtransversely to the sub-chassis 20.

[0063] Suppose now that the sub-chassis 20 is completely free to rotateabout axis 23, and suppose further that the vehicle 15 is at firsttravelling straight ahead with the main chassis 18, the sub-chassis 20,and prime mover 16 longitudinally aligned, i.e. with longitudinal axes24, 25 and 28 respectively, in line with each other. FIG. 2 shows thesituation shortly after the prime mover 16 of vehicle 15 begins a turnto the right from an original straight-ahead direction indicated byarrow 202. Because relative rotation of main chassis 18 and sub-chassis20 about axis 23 is unrestrained, the sub-chassis 20 tends to continuein direction 202, so that an angle 26, between axes 24 and 25, increasesas the vehicle 15 moves forward. In the absence of any restraint, angle26 will increase to a large value, at which unpredictable anduncontrollable behaviour will begin. However, at the early stage ofturning shown in FIG. 2, it can be said that trailer 17 is notoff-tracking inwardly in the way shown in FIG. 1 for trailer 3. To thecontrary, trailer 17 is moving toward a position outside path 27 of axis19 of the prime mover.

[0064] The arrangement shown in FIG. 2 is unstable and not practical.However, suppose now that in the vehicle 15 the rotation of thesub-chassis 20 about axis 23 is restrained in such a way that the angle26, once it reaches a chosen maximum value 26′, cannot increase further.In this case, it is found that pivot axis 23 follows a path intermediatebetween the two situations shown in FIGS. 1 and 2. For a given primemover path 27, a suitable angle 26′ can be chosen so that once a turn isestablished, pivot axis 23 will follow substantially the same path. Thatis, there will be substantially no off-tracking of the types shown inFIGS. 1 and 2. FIG. 3 shows this situation.

[0065] The value of angle 26′ which gives correct tracking in a steadyestablished turn, as shown in FIG. 3, depends on the radius of the primemover path 27, which is itself a variable chosen by a driver of thevehicle 15. Therefore, the invention provides for the angle 26′ to beset by variable stop means (preferred embodiments of which are to bedescribed in detail below) arranged so that angle 26′ varies accordingto the sharpness of turning. The sub-chassis 20 rotates about the axis23 during turns in the way described above, tending towards a straightpath, until the angle 26 reaches the value 26′ set by the stop means.

[0066] In the arrangement shown in FIG. 3, some scrubbing of wheels 21is inevitable, albeit less than in a conventional vehicle such asvehicle 1, because the wheels 21 are being prevented from rolling alonga straight path, and with three parallel axes of rotation 22, rollingwithout sliding on any curved path is not possible. The effect of wheelscrub in the situation shown in FIG. 3 is found to be that there is atorque applied to the sub-chassis 20 in a direction shown by arrow 303,which tends to increase the angle 26.

[0067] Wheel scrub during turning can be further alleviated, bycombining the above invention with a different type of sub-chassis,which will be described in outline here and in detail later. Thisdifferent sub-chassis type is also usable with other trailer steeringarrangements and is an invention in itself, independently of theinvention described above.

[0068]FIG. 4 shows a semi-trailer vehicle 29 incorporating the differentsub-chassis 33 and having a prime mover 30 and a trailer 31. The trailer31 has a main chassis 32 pivotally connected to sub-chassis 33 forrelative rotation about a substantially upright axis 349 in the mainchassis 32. To the sub-chassis 33 are mounted three rigid axles 34, 35and 36. To the axles are mounted ground-engaging wheel pairs 37, 38 and39 respectively, which have axes of rotation 40, 41 and 42 respectively.(Although three pairs of wheels are shown in FIG. 4, two or four pairscould in fact be used if required.) The axle 35 is mounted non-steerablyon the sub-chassis 33, i.e. so that the axis of rotation 41 of wheels 38is transverse to sub-chassis 33. However, axles 34 and 36 are mountedpivotally to sub-chassis 33 so that wheel pairs 37 and 39 are steerablerelative to sub-chassis 33 as shown in FIG. 4. Steering means (to bedescribed in detail below) are provided whereby, in response to thesub-chassis 33 rotating about axis 349 away from a position oflongitudinal alignment with the main chassis 32, axles 34 and 36 arecentrally pivoted so that their the axes of rotation 40 and 42 convergetoward axis 41 on one side of the sub-chassis 33. Specifically, the axes40, 41 and 42 converge towards each other on the inside of the turnbeing executed. In the idealized situation shown in FIG. 4, axes 40, 41and 42 converge with axes of rotation 43, 44 and 45 of prime moverwheels 46, 47 and 48. (Axis 45 is an average axis of rotation of thedriven wheels 48 of prime mover 30.) However, in practice perfectconvergence of the axes 40 to 42 and 43 to 45 as shown in FIG. 4 is notrequired for tracking and wheel scrub to be significantly improved bycomparison with a conventional vehicle such as vehicles 1 and 15.

[0069] In FIG. 4, angle 159′, between longitudinal axes 160 and 161 ofthe main chassis 32 and sub-chassis 33 corresponds to angle 26′ in FIG.3.

[0070] Through use of the different sub-chassis 33, rather than thesub-chassis 20, in combination with the variable stop means mentionedabove (and described below) a larger reduction in wheel scrub can beachieved while still obtaining the improved tracking that the variablestop means can provide. This is because pure rolling, as opposed tocombined rolling and sliding, of the trailer wheels 37, 38 and 39 ismore nearly approachable.

[0071] Variable Stop Means

[0072] Variable stop means will be described using as an example thevehicle 15 shown in FIG. 3. However, it is to be understood that thevehicle 29 shown in FIG. 4, with steerable axles on sub-chassis 33,could equally be used as a basis for the description, and the variablestop means is equally applicable to vehicles such as vehicle 29. Severalembodiments of the variable stop means will be described.

[0073] (a) Fully Mechanical Variable Stop Means

[0074]FIG. 5 shows in schematic plan view the vehicle 15 with primemover 16, main chassis 18 and sub-chassis 20 longitudinally aligned, asfor straight-ahead travel. Vehicle 15 is shown fitted with a fullymechanical variable stop means generally indicated as item 60. FIG. 6shows in plan view, with some structural detail omitted, a larger-scalepartial view of the vehicle 15 with means 60, now in a configurationcorresponding to a right turn.

[0075] Secured to the sub-chassis 20 via pivots 61 are two equal-lengthrods 62 a and 62 b. (The suffixes “a” and “b” here indicate separatecomponents which are the same save for being oppositely located relativeto the main chassis central axis 24. The same convention is used forother items in the following description.) The pivots 61 aresymmetrically located on opposite sides of longitudinal axis 25 of thesub-chassis 20. The rods 62 a and 62 b are pivotally connected at pivots67 to yokes 63 a and 63 b, respectively, and do not contact each otherwhere they cross (see FIG. 5). Yokes 63 a and 63 b are mounted in linearbearings 66 on the main chassis 18 and are free to slide parallel toaxis 24 of the main chassis 18. Yoke 63 a moves forward and yoke 63 bbackward as the sub-chassis 20 rotates anticlockwise (seen from above,relative to the main chassis 18) about axis 23. Conversely assub-chassis 20 rotates clockwise yoke 63 b moves forward and yoke 63 amoves backward. When sub-chassis 20 is in the straight-ahead positionshown in FIG. 5, transversely-extending slide surfaces 64 a and 64 b onyokes 63 a and 63 b are aligned, and lying against both is a slider 65.Slider 65 is pivotally mounted on a radius arm 120 which is in turnpivotally mounted to revolve about an upper extension of king pin 116 ofthe trailer 17, the kingpin 116 being coaxial with the axis 19. By meansdescribed below, radius arm 120 is arranged always to remain alignedwith axis 28 of the prime mover 16.

[0076] Accordingly, when prime mover 16 begins a right turn, radius arm120 rotates clockwise, as seen from above by an observer on the mainchassis 18, so that slider 65 moves left and forward (also as seen bythe observer) as shown in FIG. 6. At the same time, sub-chassis 20rotates anticlockwise in the way described above, so that yoke 62 amoves forward and yoke 62 b moves backward. However, the extent ofrotation of sub-chassis 20 is limited by the slide surface 64 a of yoke62 a bearing against slider 65 and it is this which sets the angle 26′,between axes 24 and 25 of the main chassis 18 and sub-chassis 20. Whenthe prime mover 16 and trailer 17 are aligned for straight-ahead travel,the value of angle 26′ is zero. As the prime mover 16 articulatesprogressively more about axis 19, angle 26′ increases continuously.During turning, what prevents sub-chassis 20 from rotating unrestrainedat angles 26 less than the value 26′ is the tendency of sub-chassis 20to continue in a straight path—enough wheel scrub develops to urgeslider surface 64 a against slider 65, although less than inconventional semi-trailer vehicle 1 executing a similar turn.

[0077] A right turn has been described above. It will be apparent thatthe symmetrical arrangement of components ensures similar operationduring left hand turns.

[0078] A number of refinements to this basic scheme are provided forenhanced effectiveness. These will now be described.

[0079] In low-speed manoeuvring particularly, a driver may suddenlydecrease the sharpness of a turn being executed by the prime mover 16.Very large forces between the slider surface 64 a (or 64 b) and slider65 can then arise, as the sub-chassis takes some travel distance toadjust to a new degree of turning. (This situation is analogous to thelarge increase in steering effort experienced by the driver of amotorcar when rapidly changing the radius of a turn at very low speeds.)To limit this effect, yokes 63 a and 63 b include identical resilientsections 68 a and 68 b respectively. FIG. 7 shows one of these, 68 a, incross-section. (The other, 68 b, is identical).

[0080] A first component 69 a slides telescopically on a co-axial secondcomponent 70 a and components 69 a and 70 a are urged apart by a coilspring 71 a between them. Rods 72 a are secured to component 69 a andfree to slide within component 70 a. Stops 73 a on rods 72 a preventcomponents 69 a and 70 a actually separating. Spring 71 a is under apredetermined compression force (preload) when components 69 a and 70 aare as far apart as stops 73 a permit. In a sudden decrease of thetightness of a turn at a low forward travel speed, excessively largeforces in the yoke 63 a do not develop, as its components 69 a and 70 aslide towards each other, compressing spring 71 a. As the turncontinues, the sub-chassis 20 adjusts to a new position. During thisadjustment process, angle 26 can temporarily exceed the angle 26′ thatcorresponds to any instantaneous position of the slider 65.

[0081] If on the other hand a sudden increase in the tightness of a turnis made, as can also happen particularly during low-speed manoeuvring,the slider 65 can cease to be in contact with slide surface 64 a (or 64b), but the sub-chassis 20 then simply rotates further, following itsnatural tendency to roll straight ahead, until contact is regained. Inthis case, the slider 65 is kept oriented correctly relative to theslide surfaces 64 a and 64 b by a link 250 which is pivotally connectedto an arm 251 on slider 65 and at pivot point 252 to main chassis 18, toform a parallelogram linkage.

[0082] The resilient sections 68 a and 68 b have another purpose. Whenthe sub-chassis 20, the main chassis 18 and the prime mover 16 arealigned straight ahead, the springs 71 a and 71 b are slightlycompressed, so that there is a small preload between surface 64 a andslider 65 and between surface 64 b and slider 65. This takes upclearances in the system, so that smooth operation is obtained withoutthe manufacturing difficulties of avoiding clearances between the yokes63 a and 63 b and slider 65.

[0083] The preloading of springs 71 a and 71 b has a consequence thatmust be dealt with. As a right turn (for example) is initiated from astraight-ahead configuration of the vehicle 15, slider 65 moveslaterally so that it remains in contact with slide surface 64 a, butleaves contact with slide surface 64 b. The preload in spring 71 b thuscauses face 64 b to move slightly forward until stops 73 b contactcomponent 70 b. As the angle of turn increases and yoke 63 a movesforward, yoke 63 b moves back so that slide surface 64 b moves back.However, for very small angles of turn, the small forward movement offace 64 b due to relaxing of preload in spring 71 b can exceed theoffsetting rearward movement of yoke 63 b, so that there is potentialfor interference between slider 65 and yoke 63 b as slider 65 returns toa central position. The opposite occurs in a left turn. This effect isavoided by a rocking latch 400 which is mounted to the main chassis 18for pivotal movement about a horizontal pin 401 which is parallel toaxis 24 of the trailer 17 and fixed in a transversely central positionin trailer 17. Latch 400 is shown in phantom outline in FIG. 6 and inFIG. 8 as seen by an imaginary observer looking along arrow 350 in FIG.6. Extraneous detail has been omitted from FIG. 8. As a right turn isinitiated, a formation 402 of slider 65 bears on the latch 400, pivotingit about pin 401 so that a part 403 b of latch 400 swings down andprevents face 64 b moving further forward than the position it has whenthe slider 65 is centralized, while a part 403 a swings up to allow yoke63 a to move forward. Thus slider 65 can be centralized withoutinterference with yoke 63 b. In a left turn, latch 400 swings the otherway so that part 403 a prevents slide surface 64 a moving forward of theposition it has when slider 65 is centralized.

[0084] It is not desirable in practice for the angle 26′ between theaxes 24 and 25 to become too large—30 degrees has been found a suitableabsolute maximum value. Suitable mechanical stops (not shown) aretherefore provided on main chassis 18 to limit left or right rotation ofsub-chassis 20. However, these do not prevent the prime mover 16 takingup angles of articulation relative to the main chassis 18 which wouldotherwise lead to larger angles 26′ than the stops permit. In suchcases, the slider 65 can simply cease to be in contact with the slidesurface 64 a or 64 b. When the prime mover 16 returns to amore-nearly-straight-ahead position, slider 65 again contacts slidesurface 64 a or 64 b.

[0085] (b) Mechanical/Hydraulic Variable Stop Means

[0086] This alternative embodiment will also be described by referenceto vehicle 15 shown in FIG. 3, again emphasizing that it is alsoapplicable to vehicle 29. Instead of the variable stop means 60, avariable stop means is provided on trailer 17 which includes subsystems410 (at rear of main chassis 18) and 411 (at front of main chassis 18).

[0087]FIG. 13 is a schematic plan view of the rear of main chassis 18with extraneous mechanical detail omitted, intended to show the layoutof major components of subsystem 410. Sub-chassis 20 is pivotallymounted to main chassis 18 for rotation about upright axis 23 and hasthree wheel pairs 21.

[0088] Sleeve members 412 a and 412 b are secured to sub-chassis 20 viapivots 413 a and 413 b, so that they can pivot about upright axes ofrotation through pivots 413 a and 413 b. Except at the pivots 413 a and413 b, sleeve members 412 a and 412 b are of tubular form. Rod members414 a and 414 b are mounted to a clevis fitting (fork) 415 and areslideable within sleeve members 412 a and 412 b. Rod members 414 a and414 b have stops 416 a and 416 b partway along their length which limitthe distance they can penetrate into their respective sleeve members 412a and 412 b.

[0089] Clevis fitting 415 is at the rear end of a slide 417 which isable to slide in a guide 418 fixed on the longitudinal centreline 24 ofmain chassis 18. Connected between the front end of slide 417 and afitting 419 fixed on the longitudinal centreline 24 of the main chassis18 is a hydraulic ram 420. As slide 417 moves forward, fluid in the headend of ram 420 is pumped into a tube 421 and fluid in a tube 422 isdrawn into the rod end of ram 420. The reverse happens as slide 417moves backward.

[0090] Referring now to FIG. 14, the subsystem 411 at the front end ofmain chassis 18 is shown in a schematic plan view with extraneous detailomitted. A shaped cam plate 423 is provided within the main chassis 18but arranged (by means described below) to rotate, relative to the mainchassis 18, in concert with the prime mover 16 about the upright axis19. That is, an observer on the main chassis 18 sees cam plate 423rotate about axis 19 relative to main chassis 18 as the prime mover 16executes turns.

[0091] A slide 424 has a cam follower roller 425 on its forward endwhich bears against shaped edge 426 of cam plate 423. Slide 424 is ableto slide within a guide 427 secured along the longitudinal centreline 24of main chassis 18. Secured to the rear end of slide 424 is a hydraulicram 428. Tubes 422 and 421 extend forward from ram 420 and are connectedto the rod end and head ends respectively of ram 428.

[0092] A third hydraulic ram 429 is provided and is single-acting, withits head end connected to tube 421 between rams 420 and 428. The pistonrod 430 of ram 429 is secured to a slider 431 which is able to slidealong guide rods 432 secured to the main chassis 18. A compression forceis maintained in piston rod 430 by preload in a coil spring 433 whichextends between slider 431 and a plate 434 on main chassis 18. By thismeans, hydraulic fluid in subsystems 410 and 411 is pressurized enoughfor sliders 417 and 424 to be urged backward and forward, respectivelyand take up clearances in subsystems 410 and 411. Specifically, when theprime mover 16, main chassis 18 and sub-chassis 20 are aligned in thestraight-ahead position, cam follower roller 425 is held in contact withedge 426 of cam plate 423, and slider 417 and rod members 414 a and 414b are pushed backwards until stopped by engagement between stops 416 aand 416 b with sleeve members 412 a and 412 b, respectively.

[0093] Cam plate 423 is lobe-shaped, with varying radius about axis 19,so that as it rotates in concert with prime mover 16, away from thestraight-ahead position to a turned position, cam follower roller 425 isable to move progressively further forward. Taking a right turn ofvehicle 15 as an example, the natural tendency of sub-chassis 20 to rollstraight ahead means that sleeve member 412 b pushes against stop 416 b,so that slider 417 moves forward and hydraulic fluid is pumped betweenram 420 and ram 428. This results in slider 424 moving forward also, amovement limited by contact between roller 425 and cam plate 423. Inthis way, allowable rotation of sub-chassis 20 is limited to an angle26′ (between axes 24 and 25) that varies with the angle between theprime mover 16 and main chassis 18.

[0094] Note that the degree of preload and the force per unit deflection(spring rate) of spring 433 are so chosen that during normal turningthere is no significant tendency for hydraulic fluid displaced from ram420 to be taken up by ram 429. However, circumstances such as sharpreductions of turning angle of the prime mover 16 at low speeds (asdiscussed above) do not lead to excess pressures in the hydraulic fluid,as ram 429 can take up fluid in these circumstances with a correspondingdeflection of spring 433. Ram 429 and spring 433 are here providing thesame function as resilient sections 68 a and 68 b of system 60. In ananalogous way, a sharp increase of turning angle at low speeds simplycauses roller 425 to separate from cam plate 423 temporarily. Whenhydraulic fluid; enters ram 429, line 422 requires make-up fluid. Thiscan be provided in several ways. One is to connect the rod end of ram429 to line 422 if rams 420, 428 and 429 have the same bore and roddiameters (not shown). Another is to vent line 422 to a reservoirmaintained at a low pressure (hydraulic accumulator) (not shown). Rams420, 428 and 429 could also be single acting.

[0095] It will be appreciated that sliders 417 and 424 could, instead ofbeing hydraulically coupled as described above, be joined by a rod (notshown) extending along axis 24 of the main chassis 18, the rod having aresilient element therein (not shown) operating on the same principle as68 a and 68 b. Such a system would be an alternative to system 60 and iswithin the scope of the invention.

[0096] Locking of Sub-Chassis to Main Chassis of Trailer

[0097] This part of the disclosure will refer to vehicle 15 and variablestop system 60, but it is equally applicable to vehicle 29 and to thealternative variable stop system 410/411. It is desirable to provide forlocking of sub-chassis 20 to the main chassis 18 in particularcircumstances. High speed forward travel is an example where it can bedesirable to have the sub-chassis 20 locked to the main chassis 18 withaxes 24 and 25 aligned. In this situation, deviations fromstraight-ahead positions of the prime mover 16 and sub-chassis 20 arevery limited. FIG. 9 (from which extraneous mechanical detail has beenomitted) shows sub-chassis 20 with a tongue 75 and locking segments 76 aand 76 b, operable by pneumatic actuators 77, 78 a and 78 brespectively, which are anchored to main chassis 18.

[0098] Tongue 75 slides in a guide 79 fixed to main chassis 18, and isfor locking sub-chassis 20 in the straight-ahead position, by enteringcooperating recess 80 in sub-chassis 20.

[0099] An air valve 81 fixedly mounted to the main chassis 18 isoperable by a formation 82 on a cam plate 83 secured to sub-chassis 20,whenever the axes 24 and 25 are within a small predetermined angle ofperfect alignment. A further air valve 84 is also fixedly mounted to themain chassis 18 (see FIGS. 6, 11) and operated by a formation 85 on anextension 86 of the radius arm 120 (or by a formation 437 on the frontof cam plate 423 in the case of subsystem 411—see FIG. 16) whenever theaxes 24 and 28 are within a small predetermined angle of perfectalignment. By suitably connecting an air supply (not shown, and normallyon the prime mover), the valves 81 and 84, and pneumatic actuator 77,actuator 77 causes tongue 75 to move into recess 80 and lock sub-chassis20 and main chassis 18 together. If a sufficiently large steering inputis made to rotate extension 86 of arm 120 and change the state of valve84, tongue 75 is withdrawn and the sub-chassis 20 can then rotate aboutaxis 23.

[0100] It is of course possible by routine means to provide that oncesub-chassis 20 is locked in the straight-ahead position as above, adeliberate operator input (other than mere steering) is required forunlocking. Thus, the vehicle 15 can if required be made to operate inthe same way as the conventional vehicle 1. A user may in this way locksub-chassis 20 in the straight-ahead position for reversing.

[0101] Irrespective of whether axes 24 and 25 are aligned, sub-chassis20 should be automatically locked to main chassis when the prime mover16 is in reverse gear. Locking segments 76 a and 76 b are provided forthis. When actuated by actuators 78 a and 78 b, they pivot rearward sothat at least one engages an arcuate rack 87 on sub-chassis 20.

[0102] Reversing can thus be done with the sub-chassis 20 and mainchassis 18 aligned, if required, or with sub-chassis 20 locked in anarticulated position, for example for tight reverse manoeuvres.

[0103] Alternatively, either or both of valves 81 and 84, 88 a may bereplaced by electric switches or other suitable transducers and theabove functionality achieved by routine means using a suitablecombination of electric/electronic and pneumatic circuitry. In aparticularly simple arrangement, the reversing light circuit can be usedto cause locking segments 76 a and 76 b to operate. Alternatively, aseparate and dedicated circuit may be used.

[0104] Alternative Sub-Chassis Arrangement

[0105] The sub-chassis 33 of the vehicle 29 will now be described, inparticular the means whereby the rigid axles 34 and 36 are alignedresponsively to pivoting of the sub-chassis 33 relative to main chassis32, so that wheels 37 and 39 “steer” in the correct sense. FIG. 10 showssub-chassis 33 schematically in plan view with extraneous mechanicaldetail omitted. FIG. 15 shows sub-chassis 33 in one possible form,adapted for use with the mechanical/hydraulic variable stop meansdescribed above (subsystems 410 and 411).

[0106] Central, non-steering rigid axle 35 is mounted transversely tothe sub-chassis 33 in conventional manner as known in the art, i.e. witha resilient suspension to allow substantially vertical movement of axle35 for absorption of road unevenness, but with the axle 35 alwaysremaining substantially transverse to the sub-chassis 33. Axle 35 isshown (FIG. 15) as being mounted via leaf springs 150 and spring/damperunits 151, but other arrangements are known in the art and may be used.

[0107] The steerable rigid axles 34 and 36 and their wheels 37 and 39respectively are mounted in essentially the same way to frames 106 and107 respectively as axle 35 is mounted to sub-chassis 33. Frames 106 and107 are mounted beneath sub-chassis 33 and are pivotable about uprightaxes 108 and 109 in the sub-chassis 33, for steering orientation ofaxles 34 and 36 and wheels 37 and 39. The mounting of axles 34 and 36 toframes 106 and 107 is by the same means as that of axle 35 tosub-chassis 33, namely via leaf springs 150 and spring/damper units151—see FIG. 15.

[0108] Links 110 and 111 respectively connect frames 106 and 107 to themain chassis 32. Links 110 and 111 connect pivots 100 and 101 secured toframes 106 and 107 respectively to pivots 102 and 103 respectively onmain chassis 32. By suitable choice of locations of pivots 100 and 101on frames 106 and 107 and pivots 102 and 103 on main chassis 32, forexample as shown in FIG. 10, pivoting steering of wheels 37 and 39 inthe requisite sense relative to sub-chassis 33, is obtainable.

[0109] In FIG. 15, pivots 100 and 101 are shown, and extend upwards fromframes 106 and 107 through slots 152 and 153 to links 110 and 111.Sub-chassis 33 is mounted to main chassis 32 via a plate 154 with aswing circle bearing 155 below. Pivots 102 and 103 are obscured in FIG.15, but are secured to the base of a member 156 which is itself securedto plate 154. Links 110 and 111 pass through clearance slots 157 in thestructure of sub-chassis 33. Pivots 413 a and 413 b of subsystem 410 areshown extending upward from sub-chassis 33 through slots 158.

[0110] In selecting pivot locations for the links 110 and 111, it isimportant to ensure that, as sub-chassis 33 pivots, the angle betweensub-chassis 33 and main chassis 32 is in fact limited by the variablestop means 410/411 (or 60). If the angles between axes 40 and 41, and 41and 42, (see FIG. 4) increase too quickly with increases in thestop-limited angle 159′ between sub-chassis 33 and main chassis 32, thiswill not occur. A lesser degree of self-steering is required, so thatthe sub-chassis 33 still pivots to an angle 159′ limited by the variablestop system but with less wheel scrubbing than in the case of thevehicle 15. The choice of suitable locations for pivot points 100, 101,102, 103 and lengths of links 110 and 111 can be made by simple trialand error to achieve suitable degrees of rotation of the axles 34 and 36for given degrees of rotation of sub-chassis 33 for a given vehiclegeometry.

[0111] Connection of Prime Mover to Variable Stop Means

[0112] The variable stop means (system 60 or 410/411) are operated by aconnection between the prime mover (16 or 30) and main trailer chassis(18 or 32). This will now be described, firstly by reference to system60.

[0113]FIGS. 11 and 12 show components whereby the slider 65 in variablestop means 60 is caused to rotate around axis 19 in concert with primemover 16 pivoting relative to trailer 17. (Reference is here being madefor convenience to vehicle 15, but the arrangement described below isequally applicable to vehicle 29.)

[0114] As best seen in FIG. 11, from which some extraneous mechanicaland structural detail has been omitted, the yokes 63 a and 63 b and theslider 65 lie between upper plate 112 of the main chassis 18 and a skidplate 113, whose lower surface 114, in use of the trailer 17, rests on“fifth wheel” 115 of the prime mover 16. A king pin 116 secured to thetrailer 17 and depending from the skid plate 113 is received and lockedin a cooperating recess 117 of the fifth wheel 115 in conventionalmanner.

[0115] A drive pin 118 parallel to the king pin 116 passes up through anarcuate slot 119 in the skid plate 113, and is secured to radius arm 120which is mounted to, and free to rotate about, an upper part of the kingpin 116 and lies between the upper plate 112 and the skid plate 113. Thedrive pin 118 is secured to fifth wheel 115 of prime mover 16 in amanner described below so that as the prime mover 16 pivots about theking pin 116, the drive pin 118 revolves in concert with prime mover 16around king pin 116. The arcuate slot 119 is centred on the king pin 116and is long enough to accommodate the maximum permitted degree ofrelative articulation of the trailer 17 and prime mover 16.

[0116] Slider 65 is mounted to an upper extension of the pin 118, and isfree to rotate around it.

[0117] For the alternative system 410/411, a simpler but similararrangement is provided—see FIG. 16. Cam plate 423 is mounted inidentical fashion to radius arm 120, for rotation about axis 19, anddrive pin 436 is secured to the base of cam plate 423 and extendsdownwards through an arcuate slot 435 in skid plate 113. Drive pin 436and slot 435 serve the same functions as drive pin 118 and slot 119.

[0118] The manner in which the drive pin 118 (or 436) is secured in afixed position relative to the fifth wheel 115 will now be described.

[0119]FIG. 12 shows the fifth wheel 115 (only) of the prime mover 16,which is of a standardized type well known in the art, having an uppersurface 121 on which the skid plate 113 of the trailer 17 rests andhaving a recess 117 for receipt of the king pin 116. The recess 117 liesat a front end of a parallel-sided slot 122 in the fifth wheel 115, andbehind the slot 122 is a tapered slot 123. When the trailer 17 is to beconnected to the prime mover 16, the tractor reverses underneath thefront end of the trailer 17 (which is supported at a suitable height forthe purpose in conventional manner) so that the trailer's king pin 116enters the tapered slot 123, then the slot 122, and is finally received(and locked by known means, not shown) in the recess 117. Finally thefront end of trailer 17 is lowered a little, so that its skid plate 113sits on upper surface 121 of the fifth wheel 115. This procedure is thesame as the procedure that would be followed for a conventional trailer.

[0120] Secured to the drive pin 118 at its lower end is a slider 552which is free to slide in a cooperating slot 553 in a wedge member 554.The direction in which the slider 552 is free to slide in member 554 isindicated by arrow “z” in FIG. 12. The slider 552 is retained captive inslot 553 by a retainer plate 555 secured to the wedge member 554 bybolts 556. A coil spring 557 is located in the slot 553 between theslider 552 and a face 558. The wedge member 554 has a tapered section559 and a parallel sided front section 560. When the trailer 17 is notconnected to prime mover 16, the wedge member 554 is held captiveimmediately below the skid plate 113, because pin 118 is secured toslider 552. As the procedure described in the preceding paragraph formating trailer 17 with prime mover 16 is followed, the wedge member 554enters the tapered slot 123 of the fifth wheel 115. When the kingpin 116reaches recess 117, the parallel-sided section 560 is received (andclosely fits) in parallel-sided slot 122. The tapered section 559 isreceived in the tapered slot 123. The spring 557 forces wedge member 554as far forward as it will go into the slots 122 and 123 and holds itthere firmly, while drive pin 118 is held at its correct radius relativeto the king pin 116 by radius arm 120.

[0121] In this way, the trailer 17 carries all the main mechanicalcomponents specific to steering of the rear sub-chassis 20, and theprime mover 16 can be conventional, with no major mechanicalmodification required for operation with the inventive trailer 17 (otherthan provision of a compressed air supply for the pneumatic componentsand minor pneumatic and/or electric components described above). This isan important practical advantage. The tapered section 559 of the wedgemember 554 may (and ideally does) taper in such a way as to match thetaper of the tapered slot 123 in fifth wheel 115. However, although thewidth of the parallel-sided slot 122 is standardized, various tapers areused in the tapered slots (such as 123) of fifth wheels, and it isdesirable for one wedge member to be usable with a range of fifthwheels. To this end, the tapered section 559 of the wedge member 554 mayhave a taper corresponding to the maximum taper expected in practice,yet still be usable with fifth wheels having more narrowly tapered slotsbecause the spring 557 causes the wedge member 554 to be forced as farforward in the fifth wheel 115 as it can go. The parallel-sided frontsection 560 is still received and firmly held in the slot 122. Thevariation which can be accommodated in practice depends on the need forthe parallel-sided front section 560 to be received far enough into theslot 122. This method of provision of a steering “input” to a trailerwithout any requirement for modification of its tractor is inventive initself.

[0122] It is of course possible to remove wedge member 554 from theslider 552 by removing plate 555 and simply sliding it off, and to thenslide on to slider 552 a new wedge member 554 of different taper,compress the spring 557 and replace plate 555.

[0123] Many variations to the above embodiments may be made withoutdeparting from the spirit and scope of the invention.

1. A trailer for use as part of an articulated vehicle, the trailerincluding: a main chassis connectable to a wheeled section of thevehicle immediately ahead of the trailer so that the trailer isrotatable relative to said wheeled section about a substantially uprightfirst axis in the main chassis; a sub-chassis having ground-engagingwheels mounted thereto, said sub-chassis being connected to the mainchassis and pivotable about a substantially upright second axis in themain chassis; stop means arranged for limiting rotation of saidsub-chassis about said second axis and away from a position oflongitudinal alignment with said main chassis, wherein said stop meansis movable responsively to relative rotation of said wheeled section andsaid main chassis about said first axis.
 2. A trailer according to claim1 having a plurality of pairs of ground engaging wheels longitudinallyspaced apart on said sub-chassis and including steering means responsiveto relative rotation of said sub-chassis and said main chassis aboutsaid second axis for steering at least one said pair relatively to saidsub-chassis in such a sense as to tend to align said sub-chassislongitudinally with said main chassis.
 3. A trailer according to claim 2wherein a said pair of steerable wheels is mounted to a rigid axle, saidaxle is pivotally mounted to said sub-chassis and said pair of wheels issteerable by pivoting of said axle about a substantially upright thirdaxis in said sub-chassis.
 4. A trailer according to claim 3 wherein saidsteering means includes a first link connecting said axle and said mainchassis.
 5. A trailer according to any one of claims 1 to 4 furtherincluding: a yoke mounted to said main chassis and bearing against saidstop means; and connecting means whereby said yoke is connected to saidsub-chassis and movable in said main chassis responsively to rotation ofsaid sub-chassis about said second axis.
 6. A trailer according to claim5 wherein: said yoke is mounted for substantially longitudinal movementin the main chassis and has a slide surface extending in a directionsubstantially transverse to the main chassis; a slider is included insaid stop means and mounted in said main chassis so as to pivot aroundsaid first axis in concert with said wheeled section pivoting about saidfirst axis; and said slide surface bears against said slider.
 7. Atrailer according to claim 6 including two said yokes and two saidconnecting means each connecting means associated with one of said yokesand wherein when the sub-chassis is aligned with the main chassis forstraight-ahead travel, the slider is located substantially at atransverse midpoint of the main chassis and respective said slidesurfaces of both yokes bear on said slider, and wherein the connectingmeans, yokes and sub-chassis are so arranged that as one said yoke movesforward the other said yoke moves backward.
 8. A trailer according toany one of claims 5 to 7 wherein the or each said connecting meansincludes a second link pivotally connected to said yoke and to saidsub-chassis.
 9. A trailer according to any one of claims 5 to 8 furtherincluding resilient means included in the or each said yoke anddeflectable responsively to a contact force between said stop means andsaid yoke.
 10. A trailer according to any one of claims 5 to 8 furtherincluding resilient means included in the or each said connecting meansand deflectable responsively to a force transmitted by said connectingmeans to or from said sub-chassis.
 11. A trailer according to any one ofclaims 1 to 4 further including: a member mounted to said main chassisfor movement relative thereto responsively to said rotation of saidsub-chassis about said second axis; and movement transmitting meanswhereby said movement of said member causes a corresponding movement ofa follower means and said corresponding movement is limited according tothe position of said stop means.
 12. A trailer according to claim 11wherein said movement transmitting means includes first and secondhydraulic actuators operatively interconnected by hydraulic fluidconduits so that actuation of said first actuator by said movement ofsaid member produces a corresponding movement by said second actuator ofsaid follower means.
 13. A trailer according to claim 12 furtherincluding a container having an internal space in fluid communicationwith a hydraulic fluid conduit connecting said hydraulic actuators andmeans whereby the volume of said space increases as hydraulic fluidpressure in said space increases.
 14. A trailer according to any one ofclaims 11 to 13 including a telescoping link having a predeterminedminimum length said link being arranged to cause said movement of saidmember responsively to said rotation of said sub-chassis in a particulardirection when telescoped to said minimum length.
 15. A traileraccording to claim 14 wherein said telescoping link is one of two suchtelescoping links respectively arranged to cause said movement of saidmember responsively to said rotation of said sub-chassis in first andsecond opposing directions.
 16. A trailer according to any one of claims11 to 15 wherein said stop means includes a cam arranged to rotate insaid main chassis about said first axis and adapted to be coupled tosaid wheeled section.
 17. A trailer according to any one of claims 1 to16 including further stop means for limiting to a fixed maximum valuesaid angular rotation of said sub-chassis about said second axis andaway from said position of alignment with said main chassis.
 18. Atrailer according to any one claims 1 to 17 further including secondlocking means whereby when said sub-chassis is in longitudinal alignmentwith said main chassis and any angular deviation from longitudinalalignment of said wheeled section and said main chassis is less than aspecified value said locking means is engageable to lock saidsub-chassis and said main chassis in longitudinal alignment for so longas said angular deviation from longitudinal alignment of said wheeledsection and said main chassis remains less than said specified value.19. A trailer according to any one of claims 1 to 18 further includingthird locking means which for so long as a reverse gear of saidarticulated vehicle is engaged locks said sub-chassis and said mainchassis at such relative angular deflection about said second axis asexists when reverse gear is engaged.
 20. A trailer for use as part of anarticulated vehicle, the trailer including: a main chassis; asub-chassis pivotable about a substantially upright first axis in themain chassis; at least one assembly pivotable about a substantiallyupright second axis in the sub-chassis and including a rigid axle withground engaging wheels thereon; and a link secured to said assembly andsaid main chassis, whereby in response to a rotation in one sense ofsaid sub-chassis about said first axis, said link rotates said assemblyabout said second axis in such a sense as to steer said wheels in such adirection as to tend to reduce said rotation of sub-chassis duringforward motion of said trailer.
 21. An articulated vehicle including atrailer according to any one of claims 1 to
 20. 22. Apparatus foroperating a ground wheel steering means of a trailer mountable to afifth wheel assembly of an articulated vehicle, said fifth wheel havinga slot in which a kingpin of said trailer is receivable and retainable,said apparatus including: a member arranged to pivot about an axis ofsaid kingpin; means whereby said ground wheel steering means is operatedresponsively to pivoting of said member about said axis; drive meanssecured to said member and which depend from said trailer and arereceivable in said slot.